A synopsis is a 1–3 sentence summary of your project.

Although it may not ever appear as an explicitly delineated section of your project documentation (and certainly not its own dedicated page), it is useful to compose an “official” project synopsis because such a summary can end up appearing in many places: at the top of READMEs, in package manager documentation, or even as part of grant proposals.

Examples

The FiPy project has a nice, direct synopsis:

FiPy is an object oriented, partial differential equation (PDE) solver, written in Python, based on a standard finite volume (FV) approach.

WAFO’s synopsis is perhaps too terse; the terms “waves” and “loads” could refer to lots of fields (in WAFO’s case, the subject turns out to be oceanography):

WAFO is a toolbox of Matlab routines for statistical analysis and simulation of random waves and random loads.

Here is a longer synopsis from GemPy, reproducing the emphasis in the original text:

GemPy is an open-source, Python-based project for generating 3D structural geological models. Utilizing an implicit modeling approach, it enables the creation of complex combinations of stratigraphical and structural features, including folds, faults, and unconformities. Moreover, GemPy is specifically designed for probabilistic modeling to tackle parameter and model uncertainties effectively.

The synopsis for Bokeh makes a point of addressing why someone might be interested in the software:

Bokeh is an interactive visualization library that targets modern web browsers for presentation. Bokeh can help anyone who would like to quickly and easily connect powerful PyData tools to interactive plots, dashboards, and data applications.

Tips

It is probably best for your synopsis to be quite matter-of-fact. It has a role to play in marketing your work, and there is some room to try to evoke positive feelings in your choice of language; but your best bet to draw in readers is to make it crystal-clear what your software does. Especially in the world of scientific software, potential users have very specific needs that they are trying to meet, and the top question on their mind will be: does your tool meet my needs?

That being said, it’s worth spending some time composing a good synopsis. If you know that you’re the kind of person that can get stuck in a rabbit-hole spending an hour debating the choice between the words “innovative” and “novel,” try giving yourself a fixed time limit, like 15 minutes, to come up with the best statement you can. You might not be fully satisfied with it, but call that “version 1” and move on. If you really keep on being bothered by it after a few days, you can always revisit.